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The room temperature electrocaloric effect is researched for (110) oriented KNbO3 film based on Landau-Devonshire theory. The phase map with different ferroelectric states is built at room temperature with the considerations of thermodynamic equilibrium conditions and minimum of thermodynamic potential. Five ferroelectric structural phases are obtained theoretically. The negative in-plane misfit strains are conducive to form the tetragonal c phase and the positive strains are in favor of the stability of tetragonal a1 and a2 phases. The electrocaloric effect relies on both misfit strain and electric field. Moreover, large electrocaloric effect is achieved in the orthorhombic phases.

A comparative study is reported on the ferroelectric ceramics with compostional formula Ba0·98La0·02Ti0·98Fe0·02O3 (BLTF1) and Ba0·97La0·02Ti0·98Fe0·02O3 (BLTF2; valency compensated). The samples were prepared by solid state route and sintered in air at 1325 °C for 4 h. The X-ray diffraction analysis confirmed the formation of tetragonal perovskite phase. The prepared samples were characterized for their dielectric and ferroelectric properties at different temperatures at 1, 5, 10 and 100 kHz. Enhancement in ferroelectric properties (Pr = 11.25 μC/cm2, Ec = 9.05 kV/cm) was observed in BLTF2 ceramics as compared to BLTF1 ceramics (Pr = 6.53 μC/cm2, Ec = 9.35 kV/cm) along with the observation of electrocaloric effect. The value of piezoelectric coefficient ‘d33’ was found to be 140 pC/N and 163 pC/N for BLTF1 and BLTF2 samples respectively. The present investigations show that the valency compensation method can improve the ferroelectric properties of the ferroelectric ceramics thereby making them more suitable for different applications.

The electrocaloric effect (ECE) is a promising candidate to replace the vapor-compression cooling technology, which has reached its end of improving the energy utilization efficiency. In the present work, the Y-modified BaTiO3 ceramics with nominal compositions of Ba(Ti1-xYx)O3 (abbreviated as BT-100xY, where x = 0.0125, 0.025, 0.0375, 0.050 and 0.0625) have been prepared through the conventional solid-state reaction sintering method. The dielectric properties and electrocaloric effect of BT-100xY ceramics have been investigated in detail. The XRD patterns indicate that all the BT-100xY ceramics possess pure perovskite structure without secondary phases. The temperature dependence of dielectric permittivity reveals that the BT-1.25Y, 2.5Y, 3.75Y and 5.0Y are normal ferroelectrics, and the BT-6.25Y is a relaxor ferroelectric. The ECE is calculated through the indirect equation based on Maxwell relation. The BT-2.5Y exhibits the largest ΔT = 1.26 K and the largest ΔS = 1.68 J/kg · K among all the BT-100xY ceramics, and the BT-2.5Y also exhibits the largest ΔT/ΔE = 0.296 × 10−6 K · m/V and the largest ΔS/ΔE = 0.394 × 10−6 J · m/kg · K∙V. The ECE in our work is comparable with or even larger than that of BaTiO3-based ceramics previously reported, which indicates that the BT-100xY ceramics are promising ECE materials.

Electrocaloric effect (ECE) is considered well applicable in the field of next generation solid state refrigeration technology. In this article, the structural properties and ECE response were altered and optimized by tailoring the Zr/Ti molar ratio in (Pb0.94La0.04)(ZrxSn0.30Ti0.70-x)O3 (x = 0.54, 0.52, 0.50 and 0.48) polycrystalline ceramics. Multiple phase transition behaviors including antiferroelectric (AFE) state to ferroelectric (FE) state transition under applied electric field, depolarization phase change behavior and AFE state to paraelectric state (PE) transition were observed, and their effects on the ECE response were investigated in detail. Significant improvement of ECE adiabatic temperature change of 1.04 K at room temperature (30 °C) was obtained by Maxwell method in (Pb0.94La0.04)(Zr0.52Sn0.30Ti0.18)O3 bulk ceramic through AFE→FE phase transition, while the highest ΔT of 2.73 K with electrocaloric strength (ΔT·ΔE−1) of 0.039 K cm kV−1 were observed in (Pb0.94La0.04)(Zr0.50Sn0.30Ti0.20)O3 bulk ceramic at temperature close to its Curie peak. The high ECE temperature change and ECE strength make them to be candidates for using in next generation solid-state refrigeration device.

Extremely high temperature in a chip will severely affect the normal operation of electronic equipment; however, the traditional air conditioning cooling technology is unsuitable for integrated circuit cooling. It is necessary to develop convenient and high-efficiency cooling techniques. In this paper, PbHfO3 antiferroelectric (PHO AFE) film was fabricated by a sol-gel method and was first found to be a promising electrocaloric (EC) material with high temperature change (ΔT ∼ -7.7 K) and acceptable EC strength (|ΔT/ΔE| ∼ 0.023 K cm kV-1) at room temperature. In addition to the negative EC effect (ECE), a large positive ECE can be observed at high temperature. The outstanding ECEs and their combination will make the PHO film one of the potential candidates for next-generation solid-state refrigeration. To understand the underlying physical mechanism for positive and negative ECEs in the PHO AFE film, a modified Ginzburg-Landau-Devonshire free-energy theory is adopted.

(Ba1−xSrx)(MnyTi1−y)O3(BSMT) ceramics withx= 35, 40 mol% andy= 0, 0.1, 0.2, 0.3, 0.4, 0.5 mol% were prepared using a conventional solid-state reaction approach. The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field (P–E) hysteresis loop measurements, respectively. The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed. The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1–0.4 mol% of manganese ions in (BaSr)TiO3(BST) specimens. A maximum electrocaloric effect (ECE) of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)−1was directly obtained at ∼21 °C and 50 kV/cm in Ba0.6Sr0.4Mn0.001Ti0.999O3sample, offering a promising ECE material for practical refrigeration devices working at room temperature.

Pb0.8Ba0.2ZrO3 (PBZ) nanofibers were prepared through electrospinning and mixed at a volume composite ratio of 0–6% with polyvinylidene fluoride (PVDF) dissolved in an organic solvent, and the PBZ/PVDF composite film was prepared through casting. The nanocomposites with PBZ nanofibers of 3 vol% showed the best ferroelectric performance in this work, and the maximum polarization value and breakdown field strength were 9.69 μC/cm2 and 420 MV/m, respectively. The dielectric constant and dielectric loss at a depolarization temperature of 285 K were 6.13 and 0.21, respectively. The performance of the electrocaloric effect was studied using the direct method near room temperature. Under 150 MV/m and − 30 °C, the △T and ΔS of the composite film were 13.99 K and 52.70 J/kg K, respectively. When the temperature increased to 70 °C, △T and ΔS become 5.08 K and 13.56 J/kg K, respectively. The simulation results and experiments indicate that the incorporation of nanofibers can increase the interface polarization with higher polarization value and improve the ferroelectric performance than pure PVDF.

The electrocaloric effect (ECE) was investigated in BaTiO3 ceramics, pure and doped with 2% of Eu3+ ions. The temperature and electric field dependences of ECE were investigated by the indirect met...

In this work, a systematic approach of waste (thermal/mechanical) energy harvesting and storage potential is studied in Ba0.85Zr0.15TiO3 (BZT) ceramics. The effect of stress on energy storage density (harvesting/storage) and electrocaloric performance is also studied. For this purpose, polarization–electric field hysteresis loops were recorded at various temperatures and uniaxial compressive stress. The Olsen cycle and electro-mechanical cycle are used for direct waste heat or mechanical energy to electrical energy conversion. A thermal energy-harvesting density of 42 kJ/m3 per cycle was obtained when the Olsen cycle was operated between 296–343 K and 0.25–1.5 MV/m. The electro-mechanical cycle-based energy harvesting is estimated as 78 kJ/m3 under the applied stress of 5–160 MPa and the electric field of 0.25–1.5 MV/m. The energy storage density is found as 39 kJ/m3 at zero stress field and 343 K, which increases to 53 kJ/m3 under the biased stress of 80 MPa in a wide operating temperature range of 296–328 K. It is observed that the high energy storage is a result of the reduction of the hysteresis loss. The electrocaloric temperature is found as 0.16 K and 0.18 K under the 0 and 80 MPa stress fields, respectively. Overall, the reported findings will enrich our understanding of the stress effect on BZT materials, which offers high performance for energy harvesting and storage-based applications. Moreover, this work can be also helpful in improving the energy storage density and electrocaloric effect via stress confinement.

Barium strontium titanate (Ba0.65Sr0.35TiO3-BST) added with a 0.5 wt% of B2O3-ZnO glass phase was prepared via a solid-state reaction approach. The lattice structures and morphologies of the ceramics were analyzed using X-ray diffraction and scanning electron microscopy technologies. The dielectric and ferroelectric properties of the glass added BST ceramics were characterized using a precision impedance analyzer and a ferroelectric polarization-electric field (P-E) hysteresis loop tester, respectively. The electrocaloric effect (ECE) was directly measured by a computer controlled thermocouple and high-voltage power supply, and also indirectly calculated using the Maxwell relation and the polarization extracted from the P-E loops as a function of temperature and electric field. The results indicate that when added with 0.5 wt% of B2O3-ZnO glass phase, the breakdown electric field of BST ceramic can be increased, and the adiabatic temperature change ΔT was enhanced from 1.70 K to 2.29 K.

Herein, 0.9(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3–0.1CaZrO3 (KNLNT–0.1CZ) relaxor system in multilayer ceramic capacitor (MLCC) are designed to attain elevated electrocaloric effect (ECE). Based on direct measurement, a large ∆T of 2.45 K is achieved in KNLNT–0.1CZ MLCC, which is nearly 10 times higher than that of ceramic counterpart. The temperature span (Tspan) on a benchmark of ∆T above 1.5 K come up to 65 °C. Such excellent ECE benefits by synergistic effect of relaxor phase transition and high electric field. This study shed light a strategy on designing new ECE materials with large ∆T and wide Tspan for solid-state cooling.

Lead‐free ferroelectric electrocaloric ceramics that could convert electrical energy into heat are the promising candidate for environment‐friendly cooling devices. For refrigeration devices, a large temperature change (ΔT) and good temperature stability are required, which are highly related to the phase structure and the applied electric field. In this work, a diffused ferroelectric–paraelectric (FP) phase transition is formed in (K, Na)NbO3 (KNN) by using appropriate composition engineering. The relaxor ferroelectrics in this work present both a large ΔT of 1.24 K and a high ΔT/ΔE of 0.19 K mm/kV. In addition, a wide temperature span exceeds 55 °C at the high electrocaloric effect (ECE) criterion (ΔT ≥ 0.5 K) could also be observed. This work not only opens a new strategy for obtaining high‐performance ceramics for refrigeration devices but also extends the application area of the KNN‐based lead‐free ferroelectrics from sensors, actuators and energy harvesting to solid‐state cooling applications.

The impact of the differing phase change characteristics on the electrocaloric effect (ECE) and thermophysical properties of Ba(ZrxTi1-x)O3 (BZT) were investigated. It is demonstrated that the ECE reduces strongly with increasing Zr concentration, from 1.25 K to 0.10 K. The strong reduction of ECE is associated with the vanishing of the latent heat as the nature of paraelectric to ferroelectric phase transition changes. Despite the second order nature of the phase transition, an enhanced electrocaloric responsivity, 0.225 × 10−6 Km V-1, occurs at the triple point composition ( x = 0.13), where the stability fields of ferroelectric phases converge. The decreasing ECE and thermophysical properties with increasing Zr concentration result in a more than one order of magnitude reduction in a caloric figure of merit, from ∼3500 J m−1s−1/2 to ∼200 J m−1s−1/2. The caloric figure of merit was used to compare the performance of other representative electrocaloric, magnetocaloric and mechanocaloric materials.

International audience; Active thermal control will be a major challenge of the twenty-first century, which has emphasized the need for the development of energy-efficient refrigeration techniques such as electrocaloric (EC) cooling. Highly polar semi-crystalline VDF-based polymers are promising organic EC materials, however, their cooling performance, which is highly structurally-dependent, needs further improvement to become competitive. Here, we report a simple method to increase the crystalline coherence of P(VDF-ter-TrFE-ter-CFE) ter-polymer in the plane including the polar direction. This is achieved by blending P(VDF-ter-TrFE-ter-CFE) with minute amounts of P(VDF-co-TrFE) co-polymer with similar VDF/TrFE unit content. This similarity allows for a cocrystallization of the co-polymer chains in the ter-polymer crystalline lamellae, preferentially extending the lateral coherence without lamellar thickening, as validated with a wide range of structural characterisation. This results in a significant dielectric and electrocaloric enhancement, with a remarkable electrocaloric effect, ΔTEC = 5.2 K, confirmed by direct measurements for a moderate electric field of 90 MV∙m-1 in a blend with 1 wt% of co-polymer.

In this work, the electrocaloric (EC) effect was studied in the (100-x)BaHf0.2Ti0.8O3-xBa0.94Sm0.04TiO3 (BHT-xBST) ceramics fabricated by the conventional solid-reaction method. By tuning composition to their diffuse phase transition (DPT), invariant critical point (ICP) and first-order phase transition (FPT), the large electrocaloric response with a temperature change of ΔT = 0.46 °C (at 64 °C) under 30 kV/cm and an electrocaloric strength of ΔT/ΔE = 0.18 K mm/kV under 12 kV/cm were achieved in BHT-70BST. In addition, BHT-50BST shows a broad EC working temperature window from 28 °C to 68 °C because of its diffusion behavior near the ferroelectric-to-paraelectric phase transition and multiphase coexistence. The maximum ΔT of BHT-50BST is larger than that of BHT-40BST with only diffusion character but no multiphase coexistence. This work may provide a design strategy to enhance EC performance with a broad working temperature region in lead-free rare-earth doped BaTiO3-based ceramics by combining the diffusion behavior, multiphase coexistence and heterovalent substitution.

Electrocaloric effect represents an environmentally friendly cooling alternative to replace the currently ubiquitous vapor-compression-based refrigeration. Previous studies have shown that large electrocaloric response is associated with the polarization change, which peaks around the phase transition temperature. However, there is only little focus on the effect of the detailed phase structure on the electrocaloric properties, particularly on the electrocaloric strength (ΔT/ΔE). For the first time, the correlation between ΔT/ΔE and the phase structure of perovskite ferroelectric materials was investigated, and a new frame to obtain optimized ΔT/ΔE related to the phase structure regulation was revealed. Given the simple and legible phase structure, BaTiO3-based ceramics are selected as a platform to reveal this relationship by employing both indirect and direct measurements. A striking variation of ΔT/ΔE and entropy change coefficient versus the electric field was first noticed at different phase structures: decreasing at the phase boundaries, whereas increasing in the pure phase regions, which could attribute to distinct entropy change mechanisms stemming from the discrepant energy profile at different phase structures. Beyond that, the maximum electrocaloric temperature change of ∼1 K and a large ΔT/ΔE of 0.48–0.25 × 10−6 K m V−1 were achieved under 5–40 kV cm−1. Also, a broad temperature span of 58 K with high ΔT/ΔE was maintained under 40 kV cm−1, and a desired electric field-stable ΔT/ΔE could be acquired. Our research provides a new paradigm for further designing and optimizing the electrocaloric performance of lead-free perovskite ferroelectrics.

The present study investigates energy storage and electrocaloric properties of lead-free barium calcium titanate (BCT) ceramics with compositions B0.80Ca0.20Ti1–3x/4FexO3 (x = 0.000, 0.005, 0.010, ...

Ferroelectric materials are attractive candidates for potential solid-state refrigeration. Their useful broad applications require investigation of several properties. However, the magnitude corresponding to electrocaloric effect (ECE) is seemingly too small. Insight from a theoretical approach is needed to provide support through theoretical description, leading mainly to better understanding and prediction of the electrocaloric performance, as well as additional properties that might be useful. Here, we investigate the elastic, electronic, thermoelectric, and ferroelectric properties as well as ECE of S n T i O 3 by utilizing first-principles calculations and effective Hamiltonian. From the calculations toward a higher symmetry direction, the direct band gap is obtained. In addition, we have comprehensively investigated the effect of M n -doping on the electronic and thermoelectric properties of S n T i O 3 to achieve a better understanding of this material. The polarization, pyroelectric coefficient, changes in entropy Δ S and adiabatic temperature Δ T are examined in detail as a function of temperature. This work also reveals the contribution with particular attention of the applied electric field especially on the magnitude of ECE, resulting in slightly anomalous volume expansion. Typical hysteresis loops are observed to confirm the order-disorder phase transition. An enhancement route of the ECE is elucidated, which may open the door for more discussions and practical applications.

Electrocaloric effect (ECE) is promising in realizing solid-state cooling as an alternative to the conventional refrigeration with environmentally harmful coolant and low efficiency. High ECE in lead-free ferroelectric ceramics is highly desirable for the EC cooling. In this work, different from the researches that tune the ECE by conventional compositional design or external stress engineering, we fabricated the (1-x)BaTiO3-xNaNbO3 (BTO-xNN) lead-free ceramics with a core-shell grain structure arising from the inhomogeneous stoichiometry of element distribution, leading to the internal compressing stress in the grains. It is interesting that the phase transition behavior, including the phase transition temperature and the diffusion property, is regulated by the core-shell grain structure induced internal stress, which can be capitalized on for the favorable ECE. Cooperated with 0.02 NN, a high ECE, e.g. adiabatic temperature change (ΔT) of 3.6 K and isothermal entropy change (ΔS) of 4.5 J kg−1 K−1, is attained in the BTO ceramic. As the internal stress further increases with more NN, the BTO-0.06NN exhibits an extremely stable ECE with a variety rate below ±4% in a wide temperature range from 300 K to 360 K. This work provides a novel approach to explore pronounced ECE in lead-free ferroelectrics for eco-friendly refrigeration.

Here, we present a collective prospective application that includes electrocaloric effect, thermal energy harvesting and energy storage density in Eu3+and Nb5+co-substituted Na0.5Bi0.5TiO3ceramics. To understand the structural property impact on desired properties, here presented the clear phase evaluation quantitatively with different phase coexistence over structural ambiguity of duel structural phase models. The induced adiabatic temperature change (ΔT) of these specimens reflects the significant change in entropy(ΔS) over a wide temperature range. The obtained change in ΔT evaluated @ 60 kV/cm was found to be nearly 0.4 K for these specimens. The pyroelectric energy harvesting property was investigated in detail with the help of the Olsen cycle. The estimated energy storage density as well as efficiency was enhanced greatly with substitution of Nb concentration as W r e c = 1.58 J/cm3 and η = 95(%) for NBET-Nb2 ceramics. The materials with multiple functionalities are considered to be an open window in the field of electronic devices, optoelectronics and solid state refrigerator applications.

The electrocaloric effect (ECE) is significantly critical for environmentally friendly cooling technologies to replace vapor compression-based refrigeration. Lead-free bismuth sodium titanate-based...

Manipulation of Curie temperature and ferroelectric polarization for enhanced room temperature electrocaloric effect (ECE) was systematically investigated in lead-free Ba1-xLaxTiO3 ferroelectric ceramics prepared by a two-step solid-state sintering technology. The experimental results and analysis showed that La dopants significantly influenced the morphology, Curie temperature, ferroelectric properties and electrocaloric effect of BaTiO3 ceramics. Especially, based on the analysis and calculation via the Maxwell relationship, a large electrocaloric strength ΔT/ΔE = 0.30 K·mm/kV near room temperature (TC = 303 K) was obtained in Ba0.96La0.04TiO3 ceramic. The present work implied an effective and reliable way to realize the room temperature electrocaloric effect in lead-free ferroelectric materials for the future application of solid-state refrigeration technology.

In an isothermal process, applying an electric field E to a ferroelectric material can change its entropy S through two distinct mechanisms: namely, through changing the dipole alignment or configurational entropy (ΔSconf), and the vibrational entropy due to the intrinsic structure response (ΔSvib). Previous numerical investigations yield only the total entropy change ΔS but cannot separate these two contributions. Here we develop a full first-principles method to extract ΔSvib and the corresponding induced adiabatic temperature change ΔTvib under E, i.e., the electrocaloric effect (ECE), and compare them to the total ΔS and ΔT from molecular dynamics simulation based on a first-principles effective Hamiltonian model. For both single crystal PbTiO3 (PTO) and PbZr0.5Ti0.5O3 (50/50 PZT), the calculation results show that for T far from the phase transition temperature Tpt, ΔSvib plays an important and even dominant role in the ECE. On the other hand, for T close to Tpt, ΔSconf dominates the ECE. Moreover, for PTO, we find that positive E can cause positive ECE, while negative E cause negative ECE. Therefore, by combining both positive and negative ECE in a “bipolar” Ericsson cycle, the cooling energy density can significantly increase as compared to that of a unipolar cycle.

This work presents the effects of sintering temperature ranging from 1200 °C to 1300 °C at intervals of 20 °C on the crystal structure, ferroelectric properties, and electrocaloric effect (ECE) of Pb0.8Ba0.2ZrO3. Samples sintered at 1240 °C, 1260 °C, and 1280 °C have large remanent polarization and small coercive field. Meanwhile, samples sintered at 1260 °C, 1280 °C, and 1300 °C possess large breakdown field strength. Samples sintered at 1260 °C for 4 h exhibit the optimal ferroelectric properties. Antiferroelectricity-ferroelectricity (AFE-FE) phase transition occurs at room temperature T1 (279 K). Directly examining ECE at this temperature is meaningful, and the temperature change is 0.068 K at approximately 60 °C and 30 kV/cm. Results laid the foundation for studying the performance of ferroelectric and ECE within this phase-transition temperature range and provide a reference for new solid-state refrigeration technology.

The influence of La3+-doping on the electrocaloric effect (ECE) of the 0.75(Pb1-3x/2Lax)(Mg1/3Nb2/3)O3-0.25(Pb1-3x/2Lax)TiO3 (L-PMN-PT: x/75/25 x = 0.0–4.0 mol.%) ceramics was studied. With the increase of La3+-doping in these ceramics, the relaxor ferroelectric properties increase, while the average grain size, coercive field E c and Curie temperature T C decrease. As a result, a maximum adiabatic temperature change Δ T as high as 0.68 K, measured by direct measurement method, was achieved under a lower electric field ( E ) intensity of 5 kV/mm at 383 K for samples with x = 2.0 mol.%. Besides the high Δ T value, the La3+-doping also leads to a temperature insensitivity of ΔT. The variation of Δ T is less than 0.15 K, or 28.3%, over a wide temperature range of 303–423 K. The La3+-doped PMN-PT ceramics, with large and temperature insensitive Δ T over a broad temperature range, is very helpful for practical application. The reduction of E c and T C can be attributed to the suppression of long-range coupling between oxygen octahedrons due to the partial replacement of Pb2+ by La3+. The temperature insensitivity of ECE is attributed to the enhancement of relaxor ferroelectric properties.

Ferroelectric perovskite materials are crucial candidates for the solid-state cooling devices due to their distinguished electrocaloric effect (ECE). Here we report the coexistence of negative and positive ECE in sol–gel derived single-layer (SL) Pb(Zr x Ti1– x O3 (PZT) thin films with a composition close to the morphotropic phase boundary (MPB). A negative ECE of $\Delta {T} = -{1.81}$ K at 135 °C and positive ECE of $\Delta {T} = {0.64}$ K at 40 °C under an applied electric field of 374 kV cm−1 are achieved. Such appearance of negative and positive ECE at different temperatures is attributed to the transition from rhombohedral to tetragonal phase and associated with the effect of defect dipoles in SL-PZT thin films at MPB.

Electrocaloric refrigeration material with good comprehensive performance such as large temperature change (ΔT), coefficient of performance (COP) and electrocaloric coefficient (ΔT/ΔE), is very attractive in the design of commercial refrigeration devices. Here, a large positive (ΔT ∼ 12.3 K with ΔS ∼ 13.6 J K−1kg−1 at 293 K) at 10 kHz and negative EC effects (ΔT ∼ - 5.8 K with ΔS ∼ - 4.5 J K−1kg−1 at ∼ 425 K) at 100 Hz are obtained in the Nb-doped Pb0.99(Zr0.65Sn0.3Ti0.05)0.98O3 antiferroelectric thin film by using a sol-gel route. Moreover, the large positive and negative EC effects are sensitive and dependent to the applied frequencies. As the applied frequency increases, the positive EC effect intends to increase. However, the negative EC effect intends to decrease as the applied frequency increases. This interesting phenomenon is ascribed to the co-coupling between the phase-transition (nanoscale tetragonal transferring into rhombohedral along the direction which is vertical to the surface of the thin film, namely the [111]) & defect dipoles. Moreover, the COP (3.37) and ΔT/ΔE (0.01 K⋅cmkV−1) are also comparable to those of previous research works. These breakthroughs and findings enable the Nb-doped PZST thin film an ideal candidate for application of next-generation solid-state cooling devices.

In this work, bismuth (Bi) and copper (Cu) doped lead lanthanum zirconate titanate (PLZT) 9/65/35 ceramics were fabricated by solid state sintering. Measurement of dielectric and ferroelectric properties at various temperatures was performed to determine electrocaloric effect in the ceramics. It was found that both undoped and doped PLZT ceramics exhibited relaxor behavior and phase transition from ferroelectric to relaxor. Indirect measurement of electrocaloric effect revealed that pure PLZT had broad peak of temperature change around the temperature at maximum dielectric constant and doped PLZT had narrower peak. Temperature change resulting from electrocaloric effect due to phase transition at low electric field could be observed in co-doped PLZT. It can be concluded that compositional effect played an important role to the change of dielectric, ferroelectric and electrocaloric properties because doping caused the change of electronic structure from A- and B-site substitution in perovskite structure of PLZT and the change of dynamic polar nanoregions.

The pseudo-first-order phase transition in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics leads to a sharp increase in temperature change (ΔT) in the vicinity of the ferroelectric-to-relaxor transition temperature TFR (~100 °C) [Appl. Phys. Lett. 110 (2017) 182904]. In this study, we add the 0.78Bi0.5Na0.5TiO3-0.06BaTiO3-0.16(Sr0.7Bi0.2)TiO3 relaxor phase to the 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ferroelectric matrix to tune its electrocaloric effect. The results show that the addition of the relaxor phase plays a vital role in phase and local-structure evolution. A transition occurs between the ferroelectric and ergodic relaxor phases when the mass fraction of the latter increases to 30% (x = 0.3), as verified by X-ray diffraction analysis, Raman spectroscopy, and polarization-electric field (P-E) hysteresis loops. Furthermore, addition of the relaxor phase reduces the TFR from 76 °C at x = 0.1–55 °C at x = 0.2; however, this transition disappears at x = 0.3 and 0.4 composite. In-situ piezo-force microscopy (PFM) images illustrate that domains can be written into x = 0.1 and 0.2 ceramics with a valley in the piezoresponse curves. Increasing the temperature agitates the domain arrangement and decreases the contrast for PFM images; this indicates a gradual phase transition in the composite. The temperature corresponding to maximum ΔT exhibits a downward shift (0.58 K at 80 °C for x = 0.1 and 0.5 K at 65 °C for x = 0.2), while the temperature-ΔT curves are flat when x = 0.3 and 0.4. Moreover, the maximum ΔT shows a decrease with an increase in the relaxor phase content; this is believed to be related to a decrease in the latent heat due to a pseudo-first-order to second-order transition. Thus, we suggest that the incorporation of a relaxor phase into ferroelectric matrices is an effective technique to tune their electrocaloric effect and improve the thermal stability of ceramic composites.

Secondary electrocaloric effect (ECE) arising from piezoelectricity combined with crystal thermal expansion was often overlooked in ECE studies of ferroelectric ceramics. This work mainly evaluated the primary ECE (ΔTECE) and secondary ECE (∆T2) of eco-friendly BaSnxTi1-xO3 (BSnT100x, 0

The direct observation of temperature changes in (Pb,La)(Zr,Ti)O3 (PLZT) (4/90/10), (8/80/20), and (8/70/30) ceramics during cycle of applying and removing electric field were utilized to evaluate ...

The manganese doped barium zirconate titanate ceramics (Ba(ZrxMnyTi1-x-y)O3-BZMT) ceramics with x = 0.15, 0.20 and y = 0, 0.0025, 0.0050, 0.0075, 0.0100, 0.0250, 0.0500 were prepared using an oxide reaction approach. The adiabatic temperature change was measured directly. Results revealed that by adjusting the nonequivalent Mn2+ ionic concentration within 0.25–0.75%, desired dielectric performances with high permittivities and lower losses were obtained. The polarization was increased with the doping content of Mn2+ ions. The largest electrocaloric temperature change obtained is 2.35 K for Ba(Zr0.15Mn0.0025Ti0.8475)O3 ceramics at 62 °C, and a broad temperature range of ∼40 °C was accompanied.

Vats et al. (2016) reported a giant negative electrocaloric effect in multi-ferroic layers. The results were deduced using the polarization from partially switched polarization loops and the Maxwell relation on the electrocaloric effect. First of all, fundamentally, the change of these polarizations with temperature, as presented in their Fig. 5, has no relation with the electrocaloric effect and hence cannot be used to deduce the ECE using the Maxwell relation. Moreover, we are troubled by the data presented in their Fig. 6, which were, as claimed by authors, deduced from the polarization data in their Fig. 5 and the Maxwell relation. We find that the ECE results presented in their Fig. 6 have no direct relation with the polarization–temperature data in their Fig. 5.

In organic multiferroics, the charge or spin coupled to the lattice induces lattice symmetry breaking, which is responsible for the ferroelectric (FE) transition. We propose a quantum spin model to describe the ferroelectricity of organic multiferroics, in which the pressure-driven spin–lattice coupling is controlled both by a jump function and a pressure power function. The T–p phase diagram shows different scaling relationships at low and high pressure regions, respectively, which is in accordance with the experimental observation. It is found that the pressure can not only enhance the FE polarization, but also enhance the transition temperature Tc as well as the electrocaloric effect (ECE). The electrocaloric critical scaling laws are proposed to verify the order and universality of the FE transition based on the Banerjee and Franco's criteria. In addition, we propose a temperature mediated mechanism within an isentropic process based on the ECE combined with the pyromagnetic effect, together with multiple physically (magnetic field and pressure jointly) controlled means, to enhance the magnetoelectric coupling around room-temperature, which will provide thermodynamic and quantum controlled means for realizing multi-state logic memory.

The phase composition and their evolution in ferroelectrics are very complex near the morphotropic phase boundary (MPB), especially under multiple fields of electric field and temperature, which results in versatile behaviors of electrocaloric effect (ECE). This paper systematically studied the phase transitions and associated ECEs in the 〈001〉, 〈011〉 and 〈111〉 oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-30PT) single crystals with the chemical composition in the MPB area. Based on the dielectric and polarization responses under multi-fields, the refined electric field-temperature phase diagrams are established, wherein the ECE properties are closely related to the electric-field-induced phase transitions and exhibit a complex evolution across positive and negative values. The negative ECE originates from the transition from a monoclinic phase to a tetragonal or orthogonal phase under the noncollinear electric field, so it only appears in the 〈001〉 or 〈011〉 oriented crystals. Conversely, the transition from the tetragonal phase to the rhombohedral or orthogonal phase in the 〈111〉 or 〈011〉 oriented crystals induces a positive ECE peak with ∆Tmax = 0.40 K (@10 kV/cm). Just above Tm, the positive ECE reaches ∆Tmax = 0.61 K, 0.63 K and 0.68 K in the 〈001〉, 〈011〉 and 〈111〉 oriented crystals, respectively. In addition, there is an abnormal net endothermic phenomenon around the monoclinic-tetragonal or monoclinic-orthogonal phase boundaries due to the electric-field-induced irreversible transition.

Pyroelectric materials are important functional materials that can generate an electrical response upon a temperature change. Among the many different types of pyroelectric materials, lead-based materials are the most widely-used traditional pyroelectric material and they will soon be banned due to their high toxicity. Therefore, in the past decade, extensive studies have been conducted to search for high performance lead-free pyroelectric materials. Recent experimental efforts have led to significant advances in lead-free pyroelectrics in different forms. This has further motivated their application from a traditional sensing function to a future energy-related prospect. This article provides a comprehensive review on the up-to-date advances in lead-free pyroelectrics, including single crystals, ceramics, inorganic films, polymers and composites. Moreover, the recent rise in energy harvesting and the electrocaloric effect as well as the potential future development of pyroelectric applications will be presented.

In this work, (Ba1−xSrx)Zr0.1Ti0.9O3 (BSZTx, x = 0, 0.15, 0.25 and 0.35) thin films were successfully deposited on La0.7Sr0.3MnO3 (LSMO)-coated (001) SrTiO3 (STO) single crystal substrates using laser molecular beam epitaxy. The BSZTx thin films with compositions of x = 0 and 0.15 display an inverse electrocaloric effect (ECE) with a maximum adiabatic temperature change of ΔT ∼ −10 K under 1500 kV cm−1, while a large positive ΔT amounting to ∼13 K is discovered in the strontium rich composition, i.e. x = 0.35. For the composition of x = 0.25 where weak ECE (|ΔT| < 2 K) is discovered, an energy storage density of 15.5 J cm−3 with an efficiency of 69.8% is observed in the temperature range of 303–413 K. The composition-tunable electrocaloric effect and large energy storage density with excellent thermal stability in strontium modified Ba(Zr0.1Ti0.9)O3 thin films are ascribed to the synergistic effects of different dynamics of polar nano-regions (PNRs) and conformed defect dipoles under large electric fields at elevated temperatures. This work will facilitate the development of novel solid-state cooling devices and provide a design route for high energy storage density devices.

The electrocaloric phenomenon in polymers and metals has gained significant interest as an alternative mechanism for conventional compressor-based refrigerators and air conditioners. This renewed interest stems from recent discoveries of new materials that can deliver a strong electrocaloric response close to room temperature. This paper presents a review of recent advances in new materials, scientific understanding, and technology demonstrations of electrocaloric polymers. Combining the advantages of the high breakdown strength of polymers and the high polarization of relaxor ferroelectric ceramic materials, ferroelectric polymer nanocomposites are promising to deliver substantially improved adiabatic change of temperature (ΔT) and isothermal change of entropy (ΔS) and markedly enhanced heating–cooling efficiency. Factors critical to the successful design of high performance electrocaloric devices for advanced flexible cooling systems, such as material combinations, structuring of nanocomposites, and device integration, are systematically reviewed. Future challenges and research opportunities for realising solid-state cooling for electronics are also discussed.

The electrocaloric effect (ECE) provides a new approach to realize environment friendly cooling with high efficiency. Although a giant ECE has been achieved in ferroelectrics, the relatively low EC strength forces conventional EC materials to be operated with very high electric fields, increasing insurmountable obstacles for pushing the ECE to become practical. Here, we reveal an extremely high EC strength (3.6 J mm K−1 kg−1 kV−1 and 0.84 K mm kV−1) in molecular ferroelectric imidazolium perchlorate (ImClO4), which is ∼13 times higher than those of the ferroelectric polymers, and also significantly exceeds those of typical inorganic displacive type ferroelectrics. The superior EC strength is attributable to the unique polarization mechanism arising from the order–disorder behavior of molecular ferroelectric ImClO4 that is completely different from conventional ferroelectrics, which is rationalized by the thermodynamic modeling. As a result, changes of entropy and temperature of 5.4 J kg−1 K−1 and 1.26 K can be attained in ImClO4 with a low electric field of 1.5 kV mm−1. This work suggests a new promising family of ferroelectrics for high-performance solid-state EC cooling.

The electrocaloric effect (ECE) of intrinsic-acceptor-doped ferroelectric system (1-x)Ba(Ti0.9Ce0.1)O3-x(Ba0.7Ca0.3)TiO3 (x = 0.3,0.5) has been studied by indirect and direct approaches. It was found that the indirect approach based on Maxwell equation is not appropriate for measuring the ECE of this acceptor-doped system. More importantly, a relatively large electrocaloric response is obtained at temperatures far below TC (maximum difference ~75 °C), which can reach 75%~90% of the maximum electrocaloric effect near TC. The unique characteristics of this acceptor-doped system have been explained by the existence of orientable defect dipoles. Our work could stimulate the design of temperature-stable electrocaloric effect through acceptor-doping.

International audience; Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) relaxor ferroelectric ceramics exhibit enhanced energy storage and electrocaloric performances due to their excellent dielectric and ferroelectric properties. In this study, the temperature-dependence of the structural and dielectric properties, as well as the field and temperature-dependence of the energy storage and the electrocaloric properties in BCZT ceramics elaborated at low-temperature hydrothermal processing are investigated. X-ray diffraction and Raman spectroscopy results confirmed the ferroelectric–paraelectric phase transition in the BCZT ceramic. At room temperature and 1 kHz, the dielectric constant and dielectric loss reached 5000 and 0.029, respectively. The BCZT ceramic showed a large recovered energy density (Wrec) of 414.1 mJ cm−3 at 380 K, with an energy efficiency of 78.6%, and high thermal-stability of Wrec of 3.9% in the temperature range of 340–400 K. The electrocaloric effect in BCZT was explored via an indirect approach following the Maxwell relation at 60 kV cm−1. The significant electrocaloric temperature change of 1.479 K at 367 K, a broad temperature span of 87 K, an enhanced refrigerant capacity of 140.33 J kg−1, and a high coefficient of performance of 6.12 obtained at 60 kV cm−1 make BCZT ceramics potentially useful coolant materials in the development of future eco-friendly solid-state refrigeration technology.

The search for new single-phase multicaloric materials, combining electrocaloric and magnetocaloric effects, is just at its beginning. Since the highest caloric effects are obtained near ferroic phase transitions, multiferroics with room-temperature ferroic anomalies are promising candidates for multicaloric cooling. In this work, such materials were prepared by tailoring the temperature of the ferroic anomalies by introducing BiFeO3, a material possessing high-temperature ferroic phase transitions, into the multicaloric Pb(Fe0.5Nb0.5)O3 to form a solid solution. A series of (1−x)Pb(Fe0.5Nb0.5)O3–xBiFeO3 (x = 0–0.5) were prepared. Among them, 0.8Pb(Fe0.5Nb0.5)O3–0.2BiFeO3 exhibits both dielectric permittivity and magnetic susceptibility anomalies at room temperature and is therefore one of the first such single-phase materials. However, at higher temperatures the material exhibits excessive Joule heating that critically degrades the electrocaloric cooling effect, while the antiferromagnetic nature of the material results in a low magnetocaloric response. Because of that, the multicaloric properties of 0.8Pb(Fe0.5Nb0.5)O3–0.2BiFeO3 were further improved by doping the material with Mn and Gd ions. This results in a composition with negligible Joule heating up to 75 °C and with room-temperature electrocaloric effect of more than 1 °C, and a high magnetocaloric effect of ∼3 °C at cryogenic temperatures. Furthermore, this material also exhibits the highest room-temperature magnetocaloric effect (∼8 × 10−3 °C) among all already known Pb(Fe0.5Nb0.5)O3-based multicalorics.

Among the unresolved issues in the study of relaxor ferroelectrics is the role of freezing temperature, across which the dynamics of polarization reversal in relaxor ferroelectrics changes. The presence of this freezing temperature is best manifested by the appearance of a double polarization hysteresis loop just above the freezing temperature. Given that the polarization pinching evolving into a double hysteresis starts well below the freezing temperature, there exists a transient temperature regime between the nonergodic and the ergodic relaxor states. To clarify the role of the freezing temperature on the pinching, the polarization reversal near the freezing temperature of relaxor (Pb1-xLax)(Zr1-yTy)1-x/4O3 (PLZT) was monitored using three in situ electric field methods: electrocaloric effect, neutron diffraction, and transmission electron microscopy. We demonstrate that the pinching results from a two-step process, 1) domain detexturization in the ferroelectric state and 2) miniaturization of domains. This observation explains the recently reported gap between the depolarization temperature Td and the ferroelectric-to-relaxor transition temperature TF-R in lead-free relaxors. We further show that Td and TF-R, which have long been considered identical in lead-based relaxors, are not the same. The current study suggests that the mismatch between Td and TF-R is an inherent feature in both lead-based and lead-free relaxor ferroelectrics. Keywords: Relaxor, Nanodomains, In situ, Neutron diffraction, Transmission electron microscopy

In this work, a pyroelectric device based on (Bi0.5Na0.5)0.94Ba0.06TiO3/graphene oxide (BNT-BT/GO) heterogeneous structures is designed and fabricated for the first time. BNT-BT/GO is obtained by a controlled Langmuir-Blodgett (L-B) assembly method, and the device for thermal-to-electrical energy conversion is fabricated from the BNT-BT/GO heterogeneous structures via an etching process. The morphology, pyroelectric properties and the thermal-to-electrical energy conversion of BNT-BT/GO have been characterized and evaluated. Notably, the fabricated BNT-BT/GO device exhibits a giant electrocaloric effect, and the refrigeration temperature change is ~7.09 K at 110 °C. More importantly, the heterogeneous structure is proved to have remarkable thermal-to-electrical energy conversion properties, whose energy density is as high as 1.361 J cm−3 with temperatures varying between 30 and 120 °C. The results demonstrate that the ferroelectric heterogeneous structures are promising for waste-heat harvesting.

Designing multicaloric single-phase materials with combined electro- and magnetocaloric effects is still at its initial stage and presents a number of challenges. One of the main challenges encountered so far is to reduce the excessive electrical conductivity, which leads to the appearance of Joule heating that might completely degrade the electrocaloric response. In this work, multicaloric Pb(Fe0.5Nb0.5)O3 material was successfully prepared exhibiting pronounced electrocaloric effect above room temperature and maximum magnetocaloric effect at cryogenic temperature. The conductivity was suppressed by controlling the sintering temperature. The ceramic sintered at 1000 °C exhibits maximum electrocaloric effective cooling of 0.88 °C at 28 °C and maximum magnetocaloric effect of 0.14 °C at −271 °C. The caloric properties can be further improved by doping Pb(Fe0.5Nb0.5)O3 with manganese. In comparison to the undoped sample, Pb(Fe0.5Nb0.5)O3 doped with 0.5 mol% of manganese exhibits three times higher maxima of electrocaloric effective cooling (2.47 °C at 80 °C) and magnetocaloric temperature change (0.44 °C at −271 °C).

Electrocaloric effect (ECE) offers a promising method for highly efficient and environment-friendly solid-state refrigeration. To obtain giant EC temperature change (ΔT), high electric field and temperature are usually applied to ECE materials, but few investigations have been done on the influence of Joule heating on ECE caused by leakage current at high electric field and temperature. In this paper, ECE, leakage current and Joule heating of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (0.5BZT-0.5BCT) ceramic were studied in the wide electric field and temperature range. The distortion of ECE curves at high electric field and temperature is proved to be caused by Joule heating which makes a negative effect on ECE refrigeration. The effective temperature change (ΔTeff) was defined, and the difference among ΔTeff, EC temperature change measured directly (ΔTD), and the intrinsic EC temperature change (ΔTECE) was discussed in detail. The results provide a guiding significance to the investigation of ECE and electronic materials.

The pyroelectric and electrocaloric effects and also the dielectric properties in a biasing electric field have been studied in lead–strontium magnoniobate–titanate solid solutions. The specific features of the temperature and field dependences of the pyroelectric and electrocaloric effects are discussed.

We have a new, effective method for direct measurements of the electrocaloric effect under arbitrary heat transfer conditions. The accuracy and reliability of measurements of the dynamics of changes in the sample temperature are due to the use of photodiode temperature sensors of the mid-IR range with the possibility of their in situ calibration.

Here, we show the large electrocaloric effect near room temperature in ergodic relaxor (Bi 1/2 Na 1/2 ) 0.93 Ba 0.07 (Zn 1/3 Nb 2/3 ) 0.01 Ti 0.99 O 3 (BNBZN) observed by a modified differential scanning calorimeter. Microstructure analysis revealed that BNBZN sample demonstrates global pseudocubic structure with locally distorted structures. Electric measurements showed that the sample coexists of two types of polar nanoregions (PNRs) with different coupling ability, and behaves as ergodic relaxor near room temperature. Due to the transition between two types of PNRs around 40 °C, large adiabatic temperature change of 1.04 °C with high electrocaloric strength of 2.1 × 10 −7 °C·m/V was recorded, indicating its promising prospect for solid-state refrigeration application.

The electrocaloric effect in ferroelectric materials has drawn much attention due to its potential applications in integrated circuit cooling and novel cooling devices. In contrast to the widely researched positive electrocaloric effect, the negative electrocaloric effect has received much less attention due to the lack of any effective methods for significant enhancement. In this work, we fabricated PbZrO3 thin film on a Pt/Si substrate by the sol-gel method. By controlling the interface conditions between the thin film and substrate, we induced defects into the interface and stabilized a transient ferroelectric phase in the PbZrO3 thin film. The emergence of the transient ferroelectric phase postpones the antiferroelectric-ferroelectric phase transition. As a result, a negative electrocaloric effect up to -18.5 K is estimated near room temperature, the highest one ever reported in this temperature range. This result suggests a new strategy to enhance the negative electrocaloric effect and may benefit the application of PbZrO3 thin films in cooling devices.